* releases/v0.16: (6003 commits)
  update CHANGELOG.md for v0.16.0
  bump version number to 0.16.0
  clingo: add `master` branch version (spack#19958)
  cmd: add `spack mark` command (spack#16662)
  spack test (spack#15702)
  Added -level_zero -rocm -opencl flags and sha256 for TAU v2.30. (spack#19962)
  Improve warning message for deprecated attributes in "packages.yaml"
  Documentation: spack load/environments prefix inspections (spack#19961)
  spack load/environments: allow customization of prefix inspections (spack#18260)
  spack containerize: allow users to customize the base image (spack#15028)
  concretizer: modified weights for providers and matching for externals
  concretizer: maximize the number of default values used for a single variant
  concretizer: don't require a provider for virtual deps if spec is external
  concretizer: spec_clauses() shouldn't emit node_compiler_hard for rule bodies.
  concretizer: don't generate rules for empty version lists
  concretizer: add a rule to avoid cycles in the graph of dependencies
  External packages have a consistent hash across different concretizers
  Don't fail if MV variants have a tuple as default value
  Fixup for target preferences
  Added unit tests to for regressions on open concretizer bugs
  ...

# Conflicts:
#	.gitignore
#	lib/spack/spack/binary_distribution.py
#	lib/spack/spack/cmd/setup.py
#	lib/spack/spack/modules/common.py
#	var/spack/repos/builtin/packages/med/package.py
#	var/spack/repos/builtin/packages/mofem-cephas/package.py
#	var/spack/repos/builtin/packages/mofem-fracture-module/package.py
#	var/spack/repos/builtin/packages/mofem-users-modules/package.py
#	var/spack/repos/builtin/packages/mpich/package.py
#	var/spack/repos/builtin/packages/petsc/package.py
#	var/spack/repos/builtin/packages/python/package.py